This invention relates to a safety clutch, particularly for use in launching life floats and the like, and of the type comprising an approximately tubular first part, an approximately cylindrical second part and a plurality of locking members in engagement with said first part, said locking members having each an abutting surface adapted to engage a corresponding abutting surface on the second part, a radially external locking surface, and being altogether adapted to co-operate with said first and second part respectively, in such a manner as to establish a releasable connection therebetween.
Such safety clutches are used in maritime relations particularly in connection with lifting and lowering manned boats, for oil drilling rigs and similar off-shore structures where the distance between the working deck and the sea surface may be up to about 50 m.
Owing to the difficult conditions frequently prevailing in such circumstances, e.g. heavy sea and strong winds rigorous demands are made on such clutches.
Said demands being imposed, partly by various safety regulations and partly by the actual conditions imply inter alia that the clutch must be releasable both in the so-called off-load state, i.e. in a partially unloaded condition, and in the so-called on-load state, i.e. when fully loaded.
The off-load case that is the normal situation occurs when the boat is to be lowered onto the sea. In case of slight sea this will not cause problems while in case of more or less heavy sea the boat will "knock" against the waves for a period of time before it has been lowered sufficiently to be supported solely by the water. In order to reduce said transitional period--which involves considerable risks to equipment as well as to personnel--clutches of the present type are used which upon activation will be released the first time their load falls below a predetermined magnitude. In reality this entails that the boat descends with a wave the first time the clutch is relieved, thereby minimizing the transitional period and the risks thereby involved.
As mentioned, in the on-load case the clutch is to be released when fully loaded. This situation is in fact identical with a situation of emergency where it is crucial to quickly have the actual connection interrupted.
In a known safety clutch of the already recited type the control member is shaped as a mantle approximately U-shaped in cross-section and mounted axially displaceable around the tubular first part. The locking wedges are arranged equidistantly around the circumference of the clutch and are pivotally journalled in the mantle by means of individual pivot pins. A spring biasses the control member and thus also the locking wedges in a direction towards the locking position. The clutch is released by displacing the control member shaped as a handle against the spring action, thereby pulling the locking wedges out of engagement with the locking groove in the central second part.
Said prior clutch, however, suffers from various disadvantages and difficulties.
Firstly, this prior clutch is not prepared for on-load release. Consequently, the clutch is to be fitted with supplementary components for that purpose in case said demand--frequently obligatory--has to be complied with.
Secondly, the clutch only offers a limited possibility of reducing the above mentioned transitional period before the boat is floating, because the withdrawal of the locking wedges necessitates a force exceeding the load-dependent force exerted on the clutch proper. This means that the clutch will not disengage until the part of the force corresponding to the weight of the boat still activating the clutch is inferior to the manually exerted force which may at a maximum correspond to operator's weight. Since the total weight of the boat typically exceeds operator's weight several times, the result is that the clutch is not released until the boat by and large is floating after all, in other words, only at the end of the critical transitional period.